Switching from qt 5.12.8 LTS to 5.15.0 LTS I found that QLineF::angle(const QLineF &line) was deprecated and angleTo() was the replacement. However they give different results. In the example attached the old angle() gives a result of 150 degrees and the new angleTo() gives a result of 210 degrees. So as they are not the same. Either a) they should be the same or b) the old angle() should not be deprecated.